Tuned Filters for Traction Rectifier Sets

Traction rectifier sets in rapid transit systems generate characteristic and uncharacteristic harmonics in the contact rail dc voltage and harmonic currents in the contact and running rails. Train control systems which use audio-frequency circulating currents in the running rails are sensitive to the harmonics generated by the rectifier sets. Mitigation of this EMI problem is possible by using tuned filters at the output of the traction rectifiers. The sources of harmonics and the design of filters to attenuate the harmonics are discussed. Two examples are given: 1) a 720/1440-Hz tuned filter for the Bay Area Rapid Transit System (BART); 2) a 1560/5160-Hz tuned filter to attenuate the EMI in the Baltimore Region Rapid Transit System (BRRTS).